A defense expert at the trial of Michael Jackson’s personal physician acknowledged Thursday that he himself would never cave in to a patient’s demand for an unsafe medical treatment, the allegation prosecutors have made against the doctor.

Dr. Robert Waldman, a specialist in addiction medicine, testified under questioning by a defense attorney that the singer was “probably” addicted to the Demerol provided by his longtime dermatologist.

But on cross-examination, a prosecutor switched the focus to the medical treatment provided by Dr. Conrad Murray, the defendant who had hired Waldman as an expert witness.

“If a patient asks you to administer a dangerous drug, a drug that could be harmful … would you refuse to administer that drug to the patient?” Deputy Dist. Atty. David Walgren asked.

“Absolutely,” Waldman replied.

Murray’s defense called the expert to bolster its theory that painkiller withdrawal caused the singer’s chronic insomnia. Jackson, the defense has suggested, was so concerned about getting sleep before crucial rehearsals that he injected himself with a lethal amount of a surgical anesthetic when Murray was out of the room. Prosecutors maintain Jackson stopped breathing after Murray set up an intravenous drip of propofol, a powerful drug intended for use only in hospitals and surgical suites, and then failed to monitor his vital signs.

Walgren noted that Jackson often went long stretches between visits to dermatologist Arnold Klein — including a full week shortly before his death. If Demerol addicts could suffer withdrawal after just eight hours, how had Jackson gone many days, the prosecutor asked.

Addicts “often have multiple sources. If they can’t get their main med, they will look elsewhere to get it,” Waldman said, adding that Klein’s records were “inadequate.”

The prosecutor seized on the answer. Have you reviewed the defendant’s records for Jackson, he asked the expert. As the jury has heard repeatedly, Murray kept no records in the months before Jackson died.

The judge directed the witness not to answer. “Assumes facts not in evidence,” Superior Court Judge Michael Pastor said.

Under further questioning by a lawyer for Murray, Waldman hinted at the frustration the defense claims the doctor encountered when he tried to get Jackson to seek help. Waldman said the best course of treatment for an addict is an inpatient treatment center, but if the person refuses “we don’t really have much choice. Hands are tied.”

Murray, 58, faces a maximum of four years in prison if convicted of involuntary manslaughter. The defense’s main scientific expert, Dr. Paul White, is to take the stand Thursday afternoon. Jurors are expected to begin deliberations next week.